Although there has been some progress in identifying the range of skills that comprise the executive neurocognitive system, their assessment has proved to be a challenge. Operationalization of executive functions (EFs) may be progressed by identifying the cognitive constructs that underlie EF test performance via principal components analysis. The underlying factor structure of 19 EF tests was examined in a non-clinical sample of 200 adults (mean age = 30.8 [18-64] years); the sample comprised 97 men. Findings revealed only weak correlations between various measures derived from the EF tests. Exploratory factor analysis revealed a model comprising six independent factors, consistent with previous reports, describing the functions of the EF system. The factors comprised: Prospective Working Memory, Set-Shifting and Interference Management, Task Analysis, Response Inhibition, Strategy Generation and Regulation, and Self-Monitoring and Set-Maintenance. Results confirm the diverse and heterogeneous nature of EFs and caution against conceptualizations that underestimate its complexity. Furthermore, variability within the "normal" executive system is evident, and further research is required to understand executive functioning in healthy populations.